Method of electroplating and product thereof



June 2, 1931. K. D.- RoBlNsoN METHOD OF ELECTROPLATING AND PRODUCT THEREOF Filed Oct. 21, 1926 cb//wgaw' /INVENTOR BY f ATTORNEYS Patented June 2, 1931 UNTTED, STATES PATENT ol-l-lciz i' KARL DAVIS ROBINSON, Fl NEW YORK, N. Y., ASSIGNOR TO THE MEIDEN GRAVURE COMPANY, OF MEBIDEN, CONNECTICUT, A CORPORATION Olj CONNECTICUT METHOD OF ELECTROPLATING AND 'PRODUCT THEBEOF Application filed October 21, 1926. Serial No. 143,803,

This invention relates particularly to an improved method of electroplating upon a metal cathode which before electroplating has received a coating of a permeable substance, and more specifically to an improved method of causing the adherence of this colloid coating to the metal, and to the product of this improved method.

The especial object of the present invention is to produce an intimate and rm adherence of the coating to the met-al on which it is coated, and to produce a deposit of metal the texture of which can be controlled by the nature of the coating andfits handling during the electroplating process.

A further object of the invention is to produce specifically a metal printing plate having firmly united thereto a printlngsurface consisting essentially of a colloid or like permeable substance.

In certain classes of printing plates, as for instance in collotype, it has been us'lal to coat a glass plate with a substratum consisting of gelatin and sodium silicate, and then coating the gelatin emulsion forming the printing surface of the plate on this substratum, the substratum adhering to the glass plate because of the common silicate content and the colloid adhering to the substratum' because of the common gelatin content. This collotype printing, however, is usually effected at comparatively low speeds and a colloid thus coated on glass is satisfactory at low speeds.

When, however, a permeable coating is applied to a metal plate, such as aluminum or zinc, and the plate is operated at high speed, the colloid coating tends to strip from the metal plate during the printing operation, and this is liable to occur even at low speed.

By the present invention, a substratum is produced containing in an intimate admixture a permeable substance as a colloid 'and a material similar to the plate, so that the colloid adheres to the metal plate in like manner as does the colloid adhere to the substratum used with a glass plate, so that these metal plates can be used at very high speed without the colloid stripping.

A preferred embodiment of the invention will now be described as employed in the pro duction of a printing plate, ,It will be understood, however, that the method is applicable for producing objects other than printing plates and therefore is not to be limited -to the production of this specific article, but

is applicable to electroplating on .a wide range of metal cathodes.

The production of a printing plate, however, will be described as illustrative only of the invention, both as to the method and product features, in which the metal plate or cathode is aluminum, the colloid is gelatin,

. and the electroplating metal is zinc.

In the accompanying drawing, Figures 1, 2 and 3 illustrate symbolically the various steps of the process, Figure 1 showing the metal plate with a colloid coating; Figure 2 the coated plate and the electrolytically deposited metal, and Figure 3 the product of Figure 2 with the addition of a printing emulsion.

Broadly considered, the method consists in utilizing the plate as the cathode and depositing upon the cathode prior to the electroplating step a thin film' of a permeable material, that is, a colloid or colloidal material permeable to the metal ion of the electrolyte, such as gelatin or other suitable colloid, which is allowed to set to the gel condition before immersion of the cathode in the electroplating bath; immersing the cathode to cause the colloid to swell to the desired condition with respect to permeability; and then passing for a suitable time, depending upon the amount of m'etal it is desired to deposit, an electric current of required amperage until this desired thickness of the metal is obtained.

As a specific example of carrying out the invention in accordance with the best practice now known to me, the cathode is in the form of an aluminum plate, which is cleaned, rinsed, dipped into a mild alkali, such as sodium carbonate solution, and then dipped in a suitable hydrochloric acid solution, this preparation of the plate being customary for preparing an aluminum plate for electroplating.

The aluminum plate thus prepared is then coated, preferably by whirling, with a solution of a suitable colloid, such as gelatin, containing preferably suiicient hydrochloric acid or other suitable acid to bring the solution into a suitable condition with respect to acidity asicompared with the acidity of the electrolyte, so that there will ybe no unde- Isired change in the physical and chemical characteristics of the gelatin when introduced into the electrolyte. That is t0 say, it is preferred that the pH of the gelatin solution be so adjusted to the pH of the electrolyte that degree of swelling and other characteristics of the gelatin reach. an equilibrium quickly when the gelatin is introduced into the electrolyte. The whirling of the plate is continued until the gelatin coating is dried. The electroplating bath in the preferred embodiment of the lnvention is slightly acid and a satisfactory bath is one of zinc sulphate, ammonium chloride and sodium acetate in suitable proportions. The colloid coated plate is immersed in the bath, which is maintained preferably at a temperature not exceeding 20 C. until the gelatin has swollen suiiiciently to have the desired permeability, ten minutes usually being suilicient for this. An

electric current of suitable amperage is then passed between the cathode plate and the anode of zinc; and the plate may be gently rubbed or swabbedduring the electroplating, which obliterates such hydrogen bubbles as penetrate the gelatin surface and will insure an even disposition of the metal. After a suliicient amount of zinc has been deposited on the aluminum plate, the plate is removed from the bath and then rinsed and dried, preferably by whirling, and if any deposits of zinc have penetrated through the face of the gelatin layer, these deposits, which are but lightly attached to deposited metal lying below the face of the gelatin layer, can be removed, without injury to the gelatin layer,

by gentle buffing while the plate is whirling after the gelatin has become dried.

This method of electroplating produces a deposit of zinc on the aluminum plate, the metallic zinc being deposited between the interstices of the permeable gelatin and becoming intimately admixed or interlaced with the gelatin coating. By this is meant that metal is deposited upon those areas of the metal plate to which the metal ion of the elec trolyte has access, the metal not being deposited upon such areas of the plate as are protected from the metal ion by the substance of the permeable membrane.

It the gelatin layer is suiliciently thick to avoid any outcropping of zinc, and if this gelatin layer is otherwise suitable for printing purposes, the plate thus formed may serve directly as a printing plate.

In the best practice of the invention, however, I prefer to. coat the plate initially with a thickness of gelatin suilicient for the purpose of providing the zinc-gelatin substratum and, after the substratum has dried, coating the plate with a colloid emulsion or coating especially prepared for printing purposes, this printing coating being applied to the prepared plate, preferably by whirling. Adhesion of this second printing coating to the substratum is eiiected by means ofthe common gelatin content, the gelatin of the printing coating adherin to the gelatin of the substratum, and the su stratumy adhering to the metal plate by reason of the metal in the substratum. This results' in the production of a plate from which the printing coating will not strip even when the plate is used at high printing speeds.

It may bestated that by a suitable choice of the colloid and its condition as to swelling, and by controlling the evolution of hydrogen at the cathode, which may be done by regulating the composition of electrolyte, current density or other suitable means, a wide control of the texture of the surface of the plate is possible. By proper control of.

the hydrogen, there will be a fine network of hydrogen bubbles formed at the surface of the metal plate, and these cause a building up of small cylinders of metal spaced in relationship to the bubbles. When this coatin is dried, as above stated, and the excess meta above the surface removed by light buling, a velvety mat surface can be obtained; and by proper control vof the hydrogen any surface from the maximum smoothness to a rough matte can be obtained.

If desired, the gelatin substratum may be removed by hot water or other suitable means, and an electroplated product obtained having a deposit of zlnc on the aluminum of a maximum smoothness or of a matte surface, which is desirable in the production of certain articles.

It will, of course, be understood that the coating used for the production of printing plates will have the characteristics which will enable the finished plate to be used for high speed printing such as ability to receive and transfer ink at high printing speeds.

While the invention has been described as particularly adapted for producing printing plates, it will be obvious that other metals both for the plate and for the metallic deposit, and other electroplating baths can be employed without departing from the invention, and that permeable membranes other than gelatin may be used depending upon the products it is desired to produce, and that the invention may be employed in the production of other products than printing plates, and the invention is therefore not to be limited to the specific details hereinbefore described.

What I claim is:

1. The method of electroplating on metal articles which consists in coating the metal with a permeable colloid prior to the electroplating step, drying the coating, causing the colloid to swell to the required condition of permeability, then plating on the article a 1Euetlal through the colloid in an electrolytic 2. The method of electroplating on metal articles which consists in coating the metal with gelatin prior to the electroplating step, drying the gelatin, causing the gelatin to swell to the required condition of permeability, and then plating on the article a metal through the gelatin in an electrolytic bath.

3. The method of electroplating on metal articles which consists in coating the metal with gelatin prior to the electroplating step, drying the gelatin, causing the gelatin to swell to the required condition of permeability, then plating on the articles a metal through the gelatin in an electrolytic bath, and drying the gelatin coating.

4. The method of producing a printing plate which consists in coating a metal plate with a permeable colloid, drying the colloid, causing the colloid to swell to the required condition of permeability, subjecting the plate and coating to an electrolytic bath containing a metallic salt, which deposits on the plate in metallic form between the interstices of the colloid, drying the applied coating, and applying a printing surface over the dried coating.

5. A printing plate having a permeable colloid coating secured thereto by electroplating with a metal through the interstices of the colloid which forms part of the finished plate.

6. A printing plate having a permeable colloid coating secured thereto by electroplating with a metal through the interstices of the colloid, and a colloid printing surface coated over the first colloid coating.

7 A printing plate having a gelatin coating secured thereto by electroplating with a metal through the interstices of the gelatin, and a printing surface coated over the gelatin.

8. An aluminum printing plate having a gelatin coating secured thereto by electroplating with zinc through the interstices of the gelatin.

9. An aluminum printing plate having a gelatin coating secured thereto by electroplatin with zinc through the interstices of the ge atin to form a substratum, and a gelatin printing surface applied over the suhstratum.

In testimony whereof, I have hereunto set my hand.

KARL DAVIS ROBINSON. 

